Deflection circuit



W B, R942. T. T. EATON 2,305,919

DEFLECTION CIRCUIT Filed Sept. 25, 1941 SEM/7100v VOL THGE GEIE/5171970@ Patented Dec. 22, 1942 SAT E S AT E Gi'ElCE DEFLECTION CIRCUIT Thomas T. Eaton, Haddon Heights, N. J., assignor to Radio Corporation of America, a corporation of Delaware 4 Claims.

My invention relates to deiiecting circuits and particularly to circuits for producing a deflecting current of saw-tooth wave shape.

An object of the invention is to provide an improved circuit of the above-described type.

A further object of the invention is to provide an improved electromagnetic deflection circuit which is compact and light in weight.

In electromagnetic deflecting circuits, it is desirable to prevent a flow of the direct current component through the deecting coils so that the deflection will not be oit center. Because of this, it is common practice to apply the required direct circuit potential to the plate of the output tube through either an iron core choke coil (employed in combination with a blocking condenser) or through the primary of an iron core transformer. This is the usual practice in vertical deiiecting circuits for television receivers or the like where the deflection is at a comparatively low frequency, such as 60 deflections per second.

In some cases, the use of a choke coil or transformer is undesirable either from the weight or economic standpoint. In such cases, the use of a pentode in place of a choke coil has been proposed. The present invention is an improvement over previous circuits employing pentodes in place of choke coils in that it greatly increases the amplitude of deecting current that it is possible to obtain from a given output tube.

In accordance with my invention, the use of the heavy iron core choke or transformer is avoided by applying the directcurrent potential to the plate of the output tube through a high impedance tube, such as a pentode, and by so varying the plate current of the pentode that a maximum amount of deflecting current is obtained. By making the control grid of the pentode increasingly negative as the saw-tooth current increases in amplitude, the amplitude of current flow through the deflecting coils may be made about twice the amplitude that can be obtained if the plate current of the pentode is held constant.

The invention will be better understood from the following description taken in connection with the accompanying drawing in which Figure 1 is a circuit diagram of a deflecting circuit embodying my invention, and

Figure 2 is a circuit diagram illustrating another embodiment of the invention.

Like parts in the two figures are indicated by the same reference characters.

Referring to Figure l of the drawing, there is illustrated a cathode ray deflecting circuit comprising a pair of deecting coils I0, an output tube II which has plate voltage applied thereto through a pentode I2, and a suitable saw-tooth voltage generator indicated at I3.

The output tube II is a pentode having high plate impedance whereby the current ow through the coils I0 will have a, good saw-tooth shape if a good saw-tooth voltage is applied to the input electrodes of tube II.

The tube I I is properly biased to function as a linear or class A amplifier, the bias being obtained, for example, by means of a cathode resistor I4 having the usual bypass condenser IE thereacross.

As well known, it is desirable to prevent the direct current component of the output from tube II from flowing through the deliecting coils I0, as such current flow would deect the cathode ray from its center position. Therefore, the D. C. flow is blocked by means of a blocking condenser II.

The D. C. plate voltage is applied to the tube II through a high plate impedance tube such as the pentode I2 which is so connected that its plate current decreases as the amplitude of the saw-tooth current wave increases. This change in plate current may be obtained by connecting a resistor 2| in series with the output tube I I and the deflecting coils IIJ to obtain a saw-tooth voltage drop thereacross which is applied to the control grid 22 of the pentode I2. It will be apparent that the control grid 22 goes more negative as the current flow through the deflecting coils increases whereby the current flow through the pentode I2 decreases. This means that substantially the entire current supplied by the output tube I I during the maximum amplitude of the saw-tooth current is current that is flowing through the deflecting coils I0.

The pentodes screen grid 24 has its operating potential applied .thereto through a resistor 25 which may have a resistance of 50,000 ohms, for example. A bypass condenser 26 holds the screen -grid 24 at the A. C. cathode potential of the pentode `to prevent Idegeneration effects.

The resistance of th-e resistor 2| depends upon the vacuum tubes being employed, but ordinarily will be from 150 ohms to several hundred ohms. Since the pentode I2 is to be operated Class A, it must be properly biased for such operation. The proper bias may in some instances be provided by the voltage drop across resistor 2|. In other cases, the bias should be increased as by means of a cathode resistor 2l suitably bypassed by a condenser 28.

In Figure 2, there is shown a delecting circuit which is the same as that of Figure l except tha-t the output tube indicated at 30 is of the low impedance type such as a triode. The use of a low impedance output tube requires that the voltage applied to its control grid have both a saw-tooth component and a pulse component as indicated by the curve 3|. This voltage wave may be generated by well known means indicated at 32. The pentode I2 functions in the circuit as previously described. If desired, proper bias may be `applied to the control grid 22 by means of a battery 33 connected either to add to or subtract from the voltage drop across resistor 2l.

'In either embodiment of the invention, the

resistor 2| preferably is so chosen the full plate current swing of the output tube will swing the pentode over its entire linear characteristic, that is, from approximately plate current cut-off to approximately zero volts on the control grid.

I claim as my invention:

1. An electromagnetic deflection circuit comprising a pair of deiiecting coils, an output tube having output electrodes, one 0f said output electrodes being an anode, means for connecting said coils to said output electrodes through an alternating current path whereby direct current cannot flow through said coils, said means including a resistor connected between said anode and said coils, a high plate impedance vacuum tube hav f ing a cathode and a control grid, means for applying a positive `direct; current potential to said anode through said high impedance tube, means connecting said cathode to the deecting coil end of said resistor and means connecting said conl trol grid to the plate end of said resistor.

2. An electromagnetic deflection circuit comprising a pair of deflecting coils, an output tube having output electrodes, one of said output electrodes being an anode, means for connecting said coils to said output electrodes through an alternating current path whereby direct current cannot flow through said coils, said means including a resistor adjacent to said anode, a high plate impedance vacuum tube having a cathode and a control grid, said cathode being connected to the deflecting coil end of said resistor and said Ycontrol grid being connected to the other end class A.

of said resistor, and means for applying a direct `current potential .to the anode of said output tube through said high impedance tube.

3. An electromagnetic deflection circuit comprising a pair of delecting coils, an output tube having an input circuit and having output electrodes, one of said output electrodes being an anode, means including a resistor and a blocking condenser for connecting said coils to said output electrodes, a high plate impedance Vacuum tube having a control electrode, means for applying a positive direct current potential to said anode through said vacuum tube, means for so applying the Voltage drop in said resistor to said control grid that the plate current of said vacuum tube is decreased in response to an increase in current flow `through said coils, and means for Iapplying a deflecting voltage to said input circuit.

4. The invention according to claim 3 wherein said output tube and said high impedance tube are so biased and adjusted that they operate THOMAS T. EATON. 

